Why are markers left in the chest of previous breast cancer patients? i can see them on x-rays and do they hurt?

Depends: These can be from prior radiation or at the site of previous surgery. These can help in the future if further treatment is needed. In the case of radiation it help to position the beam. It also pinpoints the precise area of the previous tumor. This not harmful to the pt to remain.

Risk/benefit: Leaving them in is safe and often easier than subjecting yourself to the risk of removing them. They should not be painful.

Usually clips: If the marker were one used to define a non palpable lesion for localization of tumor it should have been resected with the lesion. If the patient underwent mastectomy, the radio opaque clips are vascular clips used to control chest wall blood vessels that were bleeding during the procedure and used to stop bleeding. They are permanent and do not cause any related symptoms. and are never removed